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WO1999007635A1 - Procede de production de fluorure d'aluminium - Google Patents

Procede de production de fluorure d'aluminium Download PDF

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Publication number
WO1999007635A1
WO1999007635A1 PCT/US1998/016208 US9816208W WO9907635A1 WO 1999007635 A1 WO1999007635 A1 WO 1999007635A1 US 9816208 W US9816208 W US 9816208W WO 9907635 A1 WO9907635 A1 WO 9907635A1
Authority
WO
WIPO (PCT)
Prior art keywords
aluminum fluoride
process according
dryer
turbo
drying system
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1998/016208
Other languages
English (en)
Inventor
Klaas J. Hutter
Robert J. Danos
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Morrison Knudsen Corp
Original Assignee
Raytheon Engineers and Constructors Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Raytheon Engineers and Constructors Inc filed Critical Raytheon Engineers and Constructors Inc
Priority to AU87681/98A priority Critical patent/AU8768198A/en
Publication of WO1999007635A1 publication Critical patent/WO1999007635A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/48—Halides, with or without other cations besides aluminium
    • C01F7/50—Fluorides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

  • the present invention relates generally to improvements in the production of aluminum fluoride for use in various applications, particularly as the flux for electrolytic baths in connection with manufacturing aluminum from various ores.
  • the process of this invention results in surprising and advantageous production synergies, energy efficiency, and an aluminum fluoride product that minimizes troublesome fine particulates which can be difficult to handle.
  • Aluminum is the most widely used nonferrous metal in industrial applications.
  • Aluminum is produced from two sources: in primary aluminum production the mineral bauxite is the starting material, while in secondary aluminum production, scrap is the starting material.
  • primary aluminum production metallurgical-grade alumina is extracted from bauxite and purified through electrolysis in what is known as the Hall- Heroult process to produce aluminum.
  • the alumina is dissolved in a molten bath of cryolite.
  • Aluminum fluoride (A1F 3 ) is then typically added to the electrolytic cell solution to replace the fluorine absorbed into the cell linings and lost through volatilization.
  • hydrated alumina from a feed bin is weighted into a set of batch reaction tanks.
  • the fluosilicic acid (FSA) solution is pumped from storage tanks through a heat exchanger to the batch reaction tanks.
  • FSA fluosilicic acid
  • fluosilicic acid reacts with hydrated alumina to form a metastable, soluble form of aluminum fluoride trihydrate (alpha-form) and silica according to the following reaction (wherein “s” denotes a solid and "aq" an aqueous solution):
  • Control of process conditions in this reaction is critical to obtaining high reaction efficiencies and high product quality.
  • slurry from the reaction tanks is pumped to a silica filter.
  • Silica removed by the silica filter which discharges from the filter, is slurried in a tank and then pumped to the neutralization system.
  • the filtrate from the filter containing the aluminum fluoride in the hydrated, soluble alpha form, is sent to a green liquor holding tank from which it can be pumped to a set of precipitation tanks.
  • the concentrated aluminum fluoride trihydrate (AlF 3 *3H 2 O) is heated with steam and agitated with air to irreversibly convert the soluble alpha form of the aluminum fluoride trihydrate to the insoluble beta form according to the following sequence: (2) AlF 3 *3H 2 O (aq) — ⁇ ⁇ AlF 3 *3H 2 O (s)
  • the resulting slurry formed in the precipitator tanks is cooled before sending it to a filter feed tank.
  • the cooled slurry is pumped to a vacuum filter which separates the aluminum fluoride trihydrate (beta form) crystals from the so-called spent liquor.
  • the moist aluminum fluoride trihydrate filter cake is then fed to a flash dryer which removes free moisture and water of hydration resulting in converting at least a portion of the aluminum fluoride trihydrate to aluminum fluoride hemihydrate according to the following sequence (3):
  • the flash dryer operation may, in some applications, utilize waste heat from the calcining operation (sequence (2) above).
  • the flash dryer product is then conveyed to a calciner and cooler where the mixture of aluminum fluoride tri- further dehydrated by calcination to anhydrous aluminum fluoride per sequence (4) above, and then cooled.
  • the cooled A1F 3 product is then conveyed to an A1F 3 storage bin. From here it is loaded out by gravity to rail cars or trucks.
  • aluminum fluoride is produced by the reaction of FSA and hydrated alumina; aluminum fluoride trihydrate is crystallized from the solution; and, following separation from spent liquor, aluminum fluoride trihydrate crystals are dried and calcined to yield anhydrous aluminum fluoride. It has been found in practice, however, that the aluminum fluoride trihydrate crystals have a tendency to breakdown during drying, calcination and handling.
  • the final aluminum fluoride product thus contains a relatively high concentration of dust and fines of less than 325 mesh material that is considered an expensive nuisance during handling and processing of the material.
  • Conventional processes employing a flash dryer typically generate as much as 3-6 % of these undesired fines.
  • a general object of this invention is to provide an improved process for commercial production of aluminum fluoride from FSA and alumina.
  • a specific object of this invention is to provide a process for producing aluminum fluoride having a reduced content of fine particles.
  • a more specific object of this invention is to provide a process for producing aluminum fluoride wherein the content of fine particles below a size of about 325 mesh is less than about 1 %, preferable less than about 0.5% , by weight.
  • the invention accordingly comprises the process, involving the various components and the several steps, and the relation and order of one or more of such components or steps with respect to each of the others, as exemplified in the following detailed description and as illustrated by the drawing.
  • the improved aluminum fluoride production process of this invention comprises the coordination of an FSA-hydrated alumina process with a turbo-tray type drying system in order to improve energy efficiency, maximize crystal size, and minimize crystal breakdown.
  • waste heat from one or more of the calcining steps in the FSA-hydrated alumina process is utilized to operate a turbo- tray drying system to complete the drying of aluminum fluoride product. It has been found that this energy-efficient process also surprisingly results in an extremely low level of fines, reducing by as much as 90% or more the level of fines produced with more conventional flash drying technology.
  • Fig. 1 is a process flowchart illustrating an embodiment of the present invention.
  • FIG. 1 schematically illustrates an aluminum fluoride process utilizing a turbo-tray drying system in accordance with this invention.
  • Hydrated alumina from feed bin 10 is added to a reaction chamber 12 through feed line 14, where it is mixed with a suitable quantity of hydrofluosilicic acid fed to reactor 12 via feed line 16 from an upstream source, for example a superphosphate operation as described in the 1964 Weinrotter article.
  • Reaction chamber 12 may be provided with mixing means, such as stirrer 18, and vent means.
  • Flow stream 20 leaving reaction chamber 12 contains an aqueous solution of aluminum fluoride trihydrate in the alpha form and silica particles.
  • Flow stream 20 is directed into a solid-liquid separator 22, such as a centrifuge or filter tank.
  • Wash water may be added as needed to separator 22 via feed line 24, and hydrated silicic acid is removed through exit line 26 while the liquor containing the dissolved aluminum fluoride trihydrate is removed through exit line 28.
  • This filtrate/liquor may either be sent to a holding tank or else, as shown in Fig. 1, directly to a set of one or more crystallizers or precipitator tanks 30, 32, and 34.
  • the crystallizers or precipitator tanks 30, 32 and 34 are provided with heating means, such as steam heating jackets (not shown), to heat the contents of these units, and with agitation means, such as stirrers 31, 33 and 35 respectively.
  • heating means such as steam heating jackets (not shown)
  • agitation means such as stirrers 31, 33 and 35 respectively.
  • the soluble alpha form of the aluminum fluoride trihydrate is converted to a slurry of the insoluble beta form.
  • the slurry Exiting the crystallizers or precipitator tanks via stream 36, the slurry is cooled and directed to a second solid-liquid separator 40, such as a filter tank or centrifuge.
  • separator 40 aluminum fluoride trihydrate crystals are separated, and removed via stream 42, from the spent liquor, which is removed via stream 44. Wash water may be added as necessary to separator 40 through feed stream 46.
  • Stream 42 carrying the wet, hydrated aluminum fluoride is then directed to the top of a turbo-shelf dryer unit 50.
  • Turbo-tray or turbo-shelf dryers are generally well known in the drying art, although such technology has not previously been applied to an aluminum fluoride process, nor have the surprising benefits from so doing been recognized.
  • Various types of turbo-tray dryers are taught, for example, in U.S. Patent Nos. 3,728,797; 3,777,409; and 3,681,855; which patents are incorporated herein by reference.
  • a turbo-tray dryer such as a dryer unit 50
  • a continuous dryer consisting of a stack of rotating annular shelves in the center of which turbo-type fans revolve to circulate the air over the shelves.
  • Wet material in this case wet, hydrated aluminum fluoride, enters through the roof, falling onto the top shelf as it rotates beneath the feed opening. After completing one revolution, the material is wiped by a stationary wiper through radials slots onto the shelf below, where it is spread into a uniform pile by a stationary leveler. The action is repeated on each shelf, with transfers occurring once in each revolution. From the last shelf, material is discharged through the bottom of the dryer.
  • a steel-frame housing may consist of removable insulated panels for access to the interior. All bearings and lubricated parts are exterior to the unit with the drives located under the housing. Parts in contact with the product may be of steel or special alloy.
  • the trays can be of any sheet material, such as enameled steel, asbestos-cement composition board, or plastic-glass laminates.
  • each fan circulates air can be varied by changing the pitch of the fan blades. In final drying stages, in which diffusion controls or the product is light and powdery, the circulation rate is considerably lower than in the initial stage, in which high evaporation rates prevail. In the majority of applications, air flows through the dryer upward in counterflow to the material. In special cases, required drying conditions dictate that air flow be concurrent or both countercurrent and concurrent with the exhaust leaving at some level between solids inlet and discharge.
  • a separate cold-air supply fan may be provided if the product is to be cooled before being discharged.
  • the turbo-type tray dryer has a stack effect, the resulting draft being frequently sufficient to operate the dryer with natural draft. Pressure at all points within the dryer is typically maintained close to atmospheric. Most of the roof area is used as a breeching, lowering the exhaust velocity to settle dust back into the dryer.
  • Heating means such as a row of steam pipes, can be located in the space between the trays and the dryer housing, where they are not in direct contact with the product. High thermal efficiencies can be obtained by reheating the air within the dryer. Waste steam from the upstream calcining operation may advantageously be used as the heating medium. The high cost of heating electrically generally restricts its use to relatively small equipment. For materials which have a tendency to foul internal heating surfaces, an external heating system is employed.
  • the turbo-tray dryer can handle materials from thick slurries to fine powders. It is not suitable for fibrous materials which mat or for doughy or tacky materials. Thin slurries can often be handled by recycle of dry product. Filter- press cakes are granulated before feeding. Thixotropic materials are fed directly from a rotary filter by scoring the cake as it leaves the drum. Pastes can be extruded onto the top shelf and subjected to a hot blast of air to make them firm and free-flowing after one revolution.
  • hydrated aluminum fluoride stream 42 is fed to the turbo-tray dryer inlet 52.
  • the temperature of feed 42 to dryer inlet 52 may typically range from about 70°F to about 125 °F.
  • the temperature at the top and bottom of the dryer may typically range from about 300 °F to about 550 °F or hotter.
  • the pressure drop through the dryer is typically on the order of about 1 to 2 inches H 2 0, with the top of the dryer operated at about 0.25 to 1 inches H 2 0.
  • the dryer tray speed and the dryer turbo fan speed may each be adjusted as necessary.
  • Hot air or other gas
  • Anhydrous aluminum fluoride is recovered from the dryer outlet 56 as final product stream 60. As previously discussed, it has been discovered that this final aluminum fluoride product stream has a surprising and highly desirable low level of fines.
  • the tests performed in connection with the following examples compared the performance of a conventional flash dryer, operated in the normal manner, with a Wyssmont Turbo-Tray Dryer, Model K-20, obtained for purposes of these tests.
  • the Wyssmont K-20 dryer unit is rated at 150 lbs. of feed/hour, producing 106 lbs ./hour of dried product and running up to 44 lbs ./hour of volatiles (H 2 0).
  • the air flow rating is 122 ACFM at 575 °F, with temperature in the dryer nominally at 425 °F at the top and 450 °F at the bottom. Nominal heat consumption is approximately 390,000 BTU/hour.
  • Tests were run for several hours. For each run, samples were taken from the feed common to the flash dryer unit and the Wyssmont K-20 unit. The data and test results presented in the following examples were drawn from the test log sheets.
  • An aluminum fluoride process in accordance with the present invention was operated under the following turbo-tray dryer conditions:
  • Example 2 a total dryer residence time of about 60-70 minutes was required to produce a substantially anhydrous A1F 3 product of comparable dryness to a flash-dryer produced product.
  • the A1F 3 product was found to contain only about 0.2% by weight of fines of less than about 325 mesh. This is a dramatic improvement of a better than 90 % reduction in the presence of such fines compared with flash-dryer A1F 3 product.
  • Example 3 This example compared the A1F 3 particle size distribution (using screens of varying mesh size) for a first typical hydrated aluminum fluoride feed with the dried product resulting from processing that feed in two ways: (a) in a conventional flash dryer; and, (b) in a turbo-tray dryer in accordance with the present invention.
  • the test data is presented in Table 1 below:
  • Table 1 shows that, for the dried feed used in Example 3, a 100 mesh screen retained only 1.2% by weight of the particles in the feed, whereas a 325 mesh screen retained 98.8% by weight of the particles in the feed and passed 1.2% of the particles in the feed. The portion of the particles passed through a 325 mesh screen is what would be regarded as undesirable "fines.”
  • Example 3 When the feed of Example 3 was dried in a conventional flash dryer, the result was the production of smaller, fractured particles completely across the size distribution range, including a greater production of undesirable fines.
  • Table 1 shows that at 100, 150, 200 and 325 mesh screen sizes, a smaller percentage of the particles were retained on the screen as compared with the dried feed.
  • the percentage of fines produced in the flash dryer product approximately tripled to 3.6% , compared with 1.2% for the dried feed.
  • Example 3 when the feed of Example 3 was dried in a turbo-tray dryer in accordance with this invention, the result was the production of larger particles completely across the size distribution range, including a correspondingly smaller production of undesirable fines.
  • Table 1 shows that at 100, 150, 200 and 325 mesh screen sizes, a larger percentage of the particles were retained on the screen as compared with either the dried feed or the flash dryer product.
  • the percentage of particle fines passed by the 325 mesh screen was only one-third the corresponding percentage for the dried feed, and a surprising one-ninth the corresponding percentage for the flash dryer product.
  • Example 4 This example was comparable to Example 3 but the screen tests were performed on a second, different hydrated aluminum fluoride feed to try to confirm the surprising comparative data of Example 3. The data is presented in Table 2 below: Table 2
  • Table 2 shows that, across the entire size distribution, the flash dryer product resulted in smaller particle sizes and a correspondingly higher percentage of particle fines as compared with the dried feed (3.2% versus 1.0%).
  • the turbo-tray dryer product in accordance with the present invention resulted in larger particle sizes and a correspondingly smaller percentage of particle fines as compared with the dired feed (0.4% versus 1.0%) and, even more strikingly, as compared with the flash dryer product (0.4% versus 3.2%).

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

L'invention porte sur un procédé de séchage de fluorure d'aluminium hydraté obtenu par réaction d'alumine hydratée et d'acide silicofluorhydrique. Le séchage se fait dans une colonne à plateaux tournants pour réduire la production de particules fines et recycler l'énergie thermique des opérations d'amont. Il en résulte un fluorure anhydre d'aluminium amélioré et plus économique.
PCT/US1998/016208 1997-08-06 1998-08-05 Procede de production de fluorure d'aluminium Ceased WO1999007635A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU87681/98A AU8768198A (en) 1997-08-06 1998-08-05 Process for aluminum fluoride production

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US5485297P 1997-08-06 1997-08-06
US60/054,852 1997-08-06

Publications (1)

Publication Number Publication Date
WO1999007635A1 true WO1999007635A1 (fr) 1999-02-18

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PCT/US1998/016208 Ceased WO1999007635A1 (fr) 1997-08-06 1998-08-05 Procede de production de fluorure d'aluminium

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AU (1) AU8768198A (fr)
WO (1) WO1999007635A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108840358A (zh) * 2018-09-13 2018-11-20 衢州市鼎盛化工科技有限公司 一种制备无水氟化铝的装置及其方法
CN109707471A (zh) * 2018-12-04 2019-05-03 中冶焦耐(大连)工程技术有限公司 一种电熔镁熔坨余热利用方法及系统

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3057681A (en) * 1960-01-13 1962-10-09 Kaiser Aluminium Chem Corp Producing aluminum fluoride
US3681855A (en) * 1970-02-05 1972-08-08 Wyssmont Co Inc Nondusting,high temperature dryer
US3956147A (en) * 1973-02-17 1976-05-11 Bayer Aktiengesellschaft Production of metal fluorides from fluosilicic acid
US5707406A (en) * 1993-05-06 1998-01-13 Onoda Chemical Industry Co., Ltd. Method of manufacturing aluminum fluoride anhydride

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3057681A (en) * 1960-01-13 1962-10-09 Kaiser Aluminium Chem Corp Producing aluminum fluoride
US3681855A (en) * 1970-02-05 1972-08-08 Wyssmont Co Inc Nondusting,high temperature dryer
US3777409A (en) * 1970-02-05 1973-12-11 Wyssmont Co Inc Nondusting, high temperature dryer
US3956147A (en) * 1973-02-17 1976-05-11 Bayer Aktiengesellschaft Production of metal fluorides from fluosilicic acid
US5707406A (en) * 1993-05-06 1998-01-13 Onoda Chemical Industry Co., Ltd. Method of manufacturing aluminum fluoride anhydride

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108840358A (zh) * 2018-09-13 2018-11-20 衢州市鼎盛化工科技有限公司 一种制备无水氟化铝的装置及其方法
CN108840358B (zh) * 2018-09-13 2023-07-18 衢州市鼎盛化工科技有限公司 一种制备无水氟化铝的装置及其方法
CN109707471A (zh) * 2018-12-04 2019-05-03 中冶焦耐(大连)工程技术有限公司 一种电熔镁熔坨余热利用方法及系统
CN109707471B (zh) * 2018-12-04 2024-01-30 中冶焦耐(大连)工程技术有限公司 一种电熔镁熔坨余热利用方法及系统

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Publication number Publication date
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